The invention relates to a surgical retaining screw comprising a shaft with an external thread, a head part which is connected to the shaft securely or movably and has an interior space open towards the upper side located opposite the shaft as well as two openings which are arranged on oppositely located sides of the head part, are open towards the upper side and form a receptacle for a bar-like connecting part, and a clamping screw which can be screwed into the interior space from the upper side in such a manner that it securely clamps a connecting part placed in the receptacle in this receptacle.
Surgical retaining screws of this type can be used in various ways for stabilizing and securing bones and bone fragments in place; the surgical retaining screws can, for example, be pedicle screws. Surgical retaining screws of this type are, however, also used at other parts of the body for securing bones and bone fragments in place.
Clamping devices of very different types are known for securing a connecting part to the head part of a surgical retaining screw; for example, a clamping nut can be screwed onto a head part with an external thread (U.S. Pat. No. 5,474,555) or it is known to securely clamp the connecting parts by means of a clamping piece which can be screwed into the head part from the side (U.S. Pat. No. 6,090,111).
In other constructions, separate bearing elements, which surround the head part on the outside and into which a clamping screw is screwed, are placed on the head part (DE 41 10 002 C2; DE 41 07 480 C2; WO 2004/047657 A2; US 2005/0119667 A1).
In all these cases a relatively complicated construction results; in addition, measures must be taken to avoid any undesired spreading apart of the head part and, finally, undesired stress concentrations in the head part, as a result of which the strength can be impaired, occur in many constructions.
The object of the invention is to design a generic surgical retaining screw such that the assembly and the secure clamping of the connecting part are simplified; in addition, the strength characteristics of the arrangement are intended to be improved.